Diaphragm for sound transducers, method and apparatus for manufacturing it

ABSTRACT

Diaphragm for sound transducers and a method for manufacturing it, including providing a cellular plate-like member molded of granular starting material and defining a provisional flat front face and a rear face. A layer including said provisional flat front face is heat severed from the plate-like member, whereby a new concavely shaped front face and plate-like member is defined, where the contiguous severed cells become sealed in themselves and sealed together at the same time as they are subject to stresses and provide a hardened surface. Preferably a sheet-like member is adhered to the new front face and the curved plate-like member is then urged into substantially planar condition, whereby the sheet-like member becomes stressed and the severed cells of the new front face are subject to additional stresses, so that the resulting diaphragm has a flat front face under a higher stress than the successive cells defining said diaphragm from said front face towards said rear face, the stresses progressively decreasing from said front face towards said rear face. The invention relates also to an apparatus for severing the layer including said provisional front face, from the rest of the plate-like member.

United States Patent 1191 Bertagni 14 1 Dec. 18, 1973 DIAPHRAGM FOR SOUND TRANSDUCERS,

METHOD AND APPARATUS FOR MANUFACTURING IT Jose Juan Bertagni, 1027 Hernandaris St., Buenos Aires,

Argentina [22] Filed: June 27, 1972 [21] Appl. No.: 266,552

[76] Inventor:

Primary ExaminerStephen J. Tomsky AttorneyMilton Osheroff 57 ABSTRACT Diaphragm for sound transducers and a method for manufacturing it, including providing a cellular platelike member molded of granular starting material and defining a provisional flat front face and a rear face. A layer including said provisional flat front face is heat severed from the plate-like member, whereby a new concavely shaped front face and plate-like member is defined, where the contiguous severed cells become sealed in themselves and sealed together at the same time as they are subject to stresses and provide a hardened surface. Preferably a sheet-like member is adhered to the new front face and the curved plate-like member is then urged into substantially planar condition, whereby the sheet-like member becomes stressed and the severed cells of the new front face are subject to additional stresses, so that the resulting diaphragm has a flat front face under a higher stress than the successive cells defining said diaphragm from said front face towards said rear face, the stresses progressively decreasing from said front face towards said rear face. The invention relates also to an apparatus for severing the layer including said provisional front face, from the rest of the plate-like member.

11 Claims, 14 Drawing Figures DIAPHRAGM FOR SOUND TRANSDUCERS, METHOD AND APPARATUS FOR MANUFACTURING IT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention refers to a diaphragm to be used in sound transducers, to a method for manufacturing said diaphragm and to an apparatus for severing a layer of material from the diaphragm. More particularly, the present invention is mainly used in connection with so-called flat loudspeakers which provide an excellent high fidelity reproduction of sound, although it may likewise be used in connection with the manufacture of microphones.

In the following description, reference will be mainly made to the diaphragm of a loudspeaker, although the invention is likewise applicable to microphones.

2. Description of the Prior Art It is well known in the vibration transducing art for moving coil loudspeakers or microphones, that either the coil has to vibrate the diaphragm (in the case of a loudspeaker) or the diaphragm has to receive the vibrations and transmit them to the coil (in the case of a microphone). In both cases, the diaphragm is resiliently supported by its edge or marginal portion and has to vibrate in a plane substantially perpendicular to the axis of the coil. In other words, the coil (hereinafter called the voice coil) drives or is driven by the diaphragm in a plunger-like manner. Thus a mass of air is required in front of and behind the diaphragm and is moved thereby.

Attempts have recently been made to replace the conical diaphragm configuration, wherein the conical diaphragm is formed from paper pulp or the like, by a flat diaphragm made of an expanded cellular plastics material such as polystyrene, wherein the voice coil is mounted in a hole in the diaphragm or in a recess in said diaphragm, and the diaphragm, as such, operates in a plunger-like forward and backward vibratory manner, as in the well known above-mentioned conical diaphragms. Attempts have also been made to provide a flat diaphragm with a central funnel-shaped portion having a hole therein, in which the voice coil is secured. While all these flat lo'udspeaker embodiments operate on the same principle as the above-mentioned conical loudspeakers, the housings for these flat loudspeakers are smaller in depth.

SUMMARY OF THE INVENTION According to the present invention, there is provided a diaphragm to be used in sound transducers, comprising a strong, stiff, plastics plate-like member formed by a continuous structure of cells and having a heat severed and sealed front face, a rear face and side faces connecting said front and rear faces, the cells defining said front face being under a higher stress than the successive cells defining said diaphragm from said front face towards said rear face, the stresses progressively decreasing from said front face towards said rear face and the surface defining said front face is hardened.

The invention relates also to a method for manufac-. turing a diaphragm to be used in sound transducers made of a cellular, strong, stiff plate-like member, having a front face, a rear face and side faces connecting said front and. rear faces, said method comprises the steps of molding granular starting material to form a granular expanded-bonded, cellular, strong, heatseverable, plastics plate-like member having a provisional flat front face, said rear face and said side faces which connect said provisional flat front face with said rear face, said plate-like member defining a marginal vibration damping portion substantially circumscribing a figure portion on the rear face, said figure portion including zones of lesser thickness than said marginal vibration damping portion; severing a layer including said provisional flat front face by means of a heated, substantially filiform member by relatively moving said heated substantially filiform member through said plate-like member and thereby sealing and contracting the severed granules defining the new front face, whereby the resulting plate-like member becomes curved with a concave substantially integrally sealed front face which is hardened.

Further, according to the invention, there is provided an apparatus for severing a cellular strong stiff plastics plate-like member to'be used as a diaphragm, having a front face and a rear face, comprising a track, a heated substantially filiform member traversing said track and means for maintaining said substantially filiform member under tension.

More particularly, the filiform member is an electric wire conductor which is height adjustably mounted with regard to said track and at least one pressure means upstream of said electric wire conductor above said track adapted to urge on the plate-like member to be moved along said track in order to severe a layer therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a perspective view showing a particular embodiment of a diaphragm in accordance with the present invention.

FIG. 2 is a cross-section according to line AA of FIG. 1.

FIG. 3 is a diaphragm showing the granular arrangement of an expanded bonded cellular strong stiff plastics plate-like member.

FIG. 4 is a diagram showing the behaviour of the cells if from the plate-like member of FIG. I a top layer were to be cut by means of a cold cutter, such as a knife or a saw. This embodiment does not form part of the present invention.

FIGS. 5, 6 and 7 are respective explicative diagrams showing the behaviour of one cell which is being cut by a heated filiform member.

FIG. 8 is a diagram showing a heat severed concaveshaped plate-like member.

FIG. 9 is an actual cross-section of a concave-shaped diaphragm. FIG. 10 is a cross-sectional view of the same diaphragm of FIG. 9 which is subject to additional steps of the method of manufacture, in accordance with a further developed embodiment of the present invention.

FIG. 11 is a cross-sectional view showing the finished diaphragm mounted in a frame.

FIG. 12 is a detail in cross-sectional view of an alternative embodiment with-regard to the one shown in FIG. 14 is a diagram showing an alternative embodiment as far as the roller means are concerned in connection with the apparatus for severing a plastics platelike member, to produce the diaphragm in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With regard to the particular embodiment shown in FIGS. 1 and 2, there is shown a plate-like member 71, which is a diaphragm which has, as will be later better explained, a heat severed and solid front face 72 which is hardened and a rear face comprising a marginal vibration damping portion 73 and a central figure portion 74 which has approximately the shape of the pinna of the human ear. Within the central zone of said figure portion 74, but out of the geometric center thereof, there is a recess 75 which corresponds also to the thickest portion of the figure portion 74 and into which end a pair of parallel channels 76, 76. The periphery of the figure portion 74 is preferably of smaller thickness than the rest of the figure portion 74 and ends into an endless channel member 77 whose bottom wall 77 is to be as near as possible to the front face 72. As will be later explained, special expedients have to be provided in order to achieve the arrangement as shown in FIG. 2. The endless channel member 77 connects the periphery of the figure portion 74 with an edge or side wall 78 which ends in the marginal vibration damping portion 73. An electromagnetic unit 79 for driving the diaphragm if the assembly operates as a loudspeaker, is schematically shown as a capsule having a pair of electric conductors 80, 80. Unit 79 is to be housed into recess 75 and the conductors 80, 80 are to be housed in channel 76, 76', respectively, to be there connected to a suitable electronic circuit (not shown). Upon using the assembly as a loudspeaker, unit 79 will vibrate the figure portion 74 and thereby generate sounds, the sound generating waves of which will be blocked from movement into the marginal vibration damping portion 73 by the endless channel member 77. Preferably, the central portion including the recess 75 is stiffer than the remainder of the figure portion 74, which will improve the sound reproduction in the high frequency ranges.

The diaphragm shown in the embodiment of FIGS, 1 and 2 is manufactured by molding granular starting material to form as shown in FIG. 3 a granular expanded-bonded cellular, strong, stiff plastics plate-like member, conveniently made of polystyrene or polyurethane. The plate-like member 22 consists of expanded granules which, although in FIG. 3 they are shown as all being of substantially the same size, are in practice, not so uniform. These granules 20 are welded or fused together forming in between them alveolar cells 21 which contain moisture produced during the production of the plate-like member 22. The granules 20 are somewhat resilient. The plate-like member 22 has a substantially parallellepipedic shape and comprises a front face 23, rear face 24 and side faces 25. For the purpose of this invention it may be considered that between the front face 23 and the rear face 24 a number of layers are formed which for convenience of explanation will be defined by the rows of granules shown in FIG. 3. Thus, the front face 23 which defines a provisional front face is defined by a front face layer 26 the rear face 24 forms part of a rear face layer 27 and there are in between the layers 26 and 27 a number of intermediate layers 28, 29 and 30. Obviously in practice each layer may be formed of more than one row of granules and the granules will not be so perfectly aligned in rows as shown in FIG. 3. Due to the fact that the granules 20 are somewhat resilient and in between the granules there are the alveolar cells 21, the platelike member 22 exhibits internal damping, if a percussion force or a vibratory movement is, for instance, applied to the rear face 24, as indicated by arrow 31.

To achieve good sound reproduction it is however desirable to eliminate as far as possible this clamping effect which tends to produce distortion and reduce output.

To obtain a better output, it is advisable to remove the moisture at least from the cells facing the front face and the way this is achieved will be described later on.

There is, however, another aspect of the invention which has to be first dealt with. The granules, i.e., the granular starting material, which are to be housed in a mold in order to mold the plate-like member, 71, have a certain minimum size which is being heat expanded upon molding the plate-like member. However, the layer of granules which have to be housed in the mold cannot be below a predetermined height since otherwise, upon molding the rear face 73, 74 of the platelike member, the male stamp must remain at a certain distance from the bottom of the female mold, so that in the zone corresponding to the bottom wall 77' of the endless channel member 77, a sufficient height is maintained to assure that the plate-like member 71 has a continuous uninterrupted front face 81. To this end it is first necessary to mold a plate-like member 71 having a height as the one defined in FIG. 2 between the rear face defined by the marginal vibration damping portion 73 and the provisional front face 81 shown only in dotted lines. The resulting product is however not an optimum product, because the distance existing between the bottom wall 77 and the provisional front face 81 is too great and vibrations, particularly those corresponding to the low frequencies, would have a tendency to propagate through this portion, by-passing the endless channel member 77 and entering into the marginal vibration damping portion 73, which tends to produce distortions and reduce output.

It has been first thought to simply slice off a layer including said provisional front face 81 andcorresponding to the portion between the front face 72 and the provisional front face 81. If the slicing would be carried out for instance by a cold knife or a saw, then at least theoretically speaking the front face layer 26 would be cut into two halves, whereby one half, namely the front face layer 26 would adopt the shape as shown in FIG. 4. By proceeding along this line, the alveolar cells 21 of the front face 23 would be eliminated, provided that the severing could be carried out through those portions where the expanded granules are welded together. This would improve the output and reduce the distortions in a small proportion which is neither sufficient nor optimum.

If additional moisture present in other cells 21 could be removed, this would of course improve the qualities of the end product. It has therefore been thought that the severing should be performed by means of a heated filiform member, such as for instance a heated electric wire. The heat would then remove also an additional proportion of moisture present in underlying cells 21. Upon carrying out the tests, several unforeseeable, very surprising results were obtained and which will now be explained in connection with FIGS. 5 to 8, whereby in addition to the removal of the moisture, the resulting front face becomes automatically under a higher stress than the successive granules of the intermediate layers 28, 29, 30 and rear face layer 27. Due to the creation of these stresses, the resulting plate-like member becomes of concave shape as shown in FIG. 8 and also in FIG. 9 which represents the actual shape of the diaphragm including the features of the rear face as explained in connection with FIG. 1. In addition, the surface defining said front face 72 becomes sealed and hardened. I i

In order to explain the results which were achieved by the tests, reference will now be made to a thedry which has been deduced from the results of the tests and which is believed to be the reason for achieving such an unforeseeable result. To explain this theory, reference will first be made to a single expanded granule as shown in FIG. 5, which before being subject to the heat severing process, will for this theory be considered as if it were a substantially perfect sphere, as indicated in part by dotted line 82. Axis line 83 indicates a cutting plane through which the electrically heated wire 84 is to move.

It has to be borne in mind that the granule 20',i if made for instance of polystyrene, upon being cut by heat, produce at the cutting surface fiber-like filaments which melt due to the heat and form thereby a new layer at the heat severed surface. As soon as the heated wire 84 enters in contact with the granule 20', there is a retraction bearing in mind that it is an expandbd granule of the granule in the zone adjacent the wire 84, which can be seen in FIG. 5 by comparing the full line drawing with the dotted line 82. This movement; is somewhat resisted particularly by the lower portion of the granule due to the fact that it has to be recalled that the lower portion of the front face layer 26 see also 26' of FIG. 4 is connected to the next intermediate layer 28 which are also subject to the heat effect, so that the moisture present'in the adjacent cells 21 islat the same time substantially removed. As the wire 84 continues its movement, as shown in FIG. 6, those fibers which tend to be formed adjacent the cutting zone, by the same heat, fall onto the cut portion, thereby increasing the thickness of this layer and hardening the same. This is represented by means of a thicker line 85 which, for simplicity, has likewise been shown in the upper portion, although in practice the upper portion is of no importance because the sliced-off part which corresponds to the section encircled by the dotted line in FIG. 2 is disposed of. The forward movement of the heated'wire 84 produces an additional tensile stress in the direction of movement of the wire 84 along the granule 20', so that the end 86 moves further away from the dotted line 82. This process is continued FIG. 7 until the heated wire 84 has passed through the granule 20' dividing the latter into two halves 20a, 20b. The lower half 20a has a concave-shaped severed surface 86 created by the stresses and the same is true for the upper half 20b, although the latter, since it is not linked to the additional intermediate layers, has a tendency to return to its original shape due to the memory of the material. The lower half 20a remains with a higher stress because due to the heat effect the immediate adjacent granules have likewise changed their shape. This stress, as will be later explained in connection with FIG. 8, changes also the shape of the immediate adjacent layers 28, 29, 30 of granules see FIG. 8. If the process just described is repeated through a chain of welded adjacent granules, a shrinking tendency is produced, which transforms the flat-plane plate-like member 22, into a concave-shaped plate-like member 87, as shown in FIG. 8. The severed front layer 26" is the one which shrinks most while the rear face layer 27 has not been substantially subject to any transformation. Therefore, the plate-like member behaves like a loaded beam member resting on spaced 7 apart supports, at least up to the neutral line thereof.

Thus, automatically, the successive layers 28, 29, 30 and 27, defining successive rows of cells have progressively decreasing stresses from the front face 72' towards the rear face 24'. This method further automatically seals the front face 72'. Thus, no extra sealing step is necessary, at least as far as the front face 72 is concerned. Therefore, as a result of the method, the surface defining the front face 72' is a hardened skinlike surface integral with said plate-like member 22 and sealing the front face.

While FIG. 8 merely shows the behaviour of the granules of the different rows to illustrate the progressively decreasing stress arrangement, it will readily be understood that in practice the resulting diaphram 88 will have the shape as shown in FIG. 9, where the bottom wall member 77 is now at the smallest possible distance with regard to the front face 72'. By smallest possible distance" is to be understood that a thickness is provided which allows the figure portion 74 to vibrate without a breakage occurring in the portion adjacent the bottom wall member 77'. This size cannot be achieved by direct molding, but only by severing the exceedent layer in the way as just explained.

Tests have been made with the diaphragm 88 of FIG. 9, to which the electromagnetic unit 79 see FIG. 1 has been attached and the results achieved may be classified as quite good. The fact that the front face 72 is hardened is an additional feature which increases the stresses, bearing in mind that the quality of the sound reproduction will become better if the stresses in the front face are increased, so that said front face will act as a tensioned height of a drum.

To this end, as shown in FIG. 10, the front face is covered with a sheet member 32 having marginal portions 33 projecting beyond the front face 72.

The sheet member 32 may for instance be made of paper or fabric. The face opposite the one to be adhered to the front face 72' may have a suitable decoration or design.

It is now possible to apply to the granules 20 a second stress, parallel to the planes defined by the layers. To this end, the curved plate-like member of FIG. 10 is now urged, with the adhered sheet-like member 32, into substantially planar condition as shown in FIG. 1 1. Since the granules are now also tensioned in planes parallel to their layer, they will become somewhat more flattened, so that thereby the total thickness of the plate-like member 22 is further reduced. Simultaneously, the sheet member 32 is also stretched in its own plane and in order to anchor the sheet member in its stretched state, the marginal portions 33 are now adhered at least to the side faces 25. If the length of the marginal portions 33 is. somewhat larger, they may be turned over to cover the edge portions of the rear face 24, without degrading the resulting diaphragm.

Thus, a flat diaphragm with pre-tensioned layers is obtained, in which the tension gradually decreases from layer to layer between the front face and the rear face. The diaphragm is kept fiat by linking it to a frame The double tensioned diaphragm 71, as shown in FIGS. 1 and 11, provides therefore a still better result in sound reproduction. For clarity purposes, in FIG. 1 the frame 89 has not been shown.

The embodiment of FIG. 12 differs over the embodiment of FIG. 11 in that the double tensioned diaphragm 71 has been urged to a substantial planar condition by means of frame 89' without thediaphragm having adhered thereto the sheet member. If desired, a, preferably pre-tensioned, sheet-like member 32 is stressed on the frame 89' above, and preferably spaced apart from, the front face 72'. This sheet-like member 32 is provided for decorative purpose, although if the spacing between said sheet member 32 and the front face 72 is reduced to a minimum, they enter in cooperative relationship if the vibrations are substantial upon the front face 72 contacting the sheet member 32.

In FIG. 13 an apparatus is shown which can be used for severing the plate-like member according to the method as previously described. The apparatus comprises a U-shaped casing 90 defining a track 91 on which a conveyor platform 92 moves forward and backward by means of a schematically indicated driving arrangement 93. This driving arrangement 93 consists of a driving roller 94 and a driven roller 95 having cable means 96 linked to the conveyor platform 92 to move the latter in either of the directions as indicated by double arrow 97. Above track 91 preferably a roller 98 in height adjustably arranged in schematically shown bearings 99. Downstream of roller 98, a heated filiform member, more particularly an electric wire 100 is arranged between a stationary height adjustable post 101 and a roller 102 over which said wire 100 runs and supports at its free end a weight 103. Thus, the wire 100 is always under a suitable tension. Roller 102 as well as post 101 are connected through wires 104 and 105 to an electricity supply source 106. Roller 102 is likewise height adjustably supported by casing 90 only schematically indicated by double arrow 107. Air cooling nozzles 108, 109, are provided adjacent the post 101 and roller 102.

The operation of the apparatus is as follows: the platform 92 is moved-upstream beyond the roller 98 and a plate-like member is mounted on said platform 92 which is now moved downstream passing by the roller 98 which exerts a slight pressure on the front face 23 to bypass the electrically heated wire 100 and severe the upper layer, whereby the front face 72 is formed at the same time as the resulting diaphragm becomes concavely shaped, to result in a product as shown in FIG. 9. The diaphragm 88 is unloaded then from the platform 92 and subject to further treatments, as explained in connection with FIGS. and 11 as previously explained. The platform is then moved upstream to receive a new load. It can be readily conceived that if two rollers 98 are provided on each side'of the electric wire 100, that then during each stroke a working operation may be performed, provided that the other roller is withdrawn to become inoperative.

The system of the platform 92 is merely illustrative. It could be replaced by rollers such as shown in FIG. 14. More particularly, the bottom rollers 110, 111, move the plate-like member 22 in the direction indicated by arrow 112 and the arrangement of rollers 1 10 and 111 with regard to the electric wire and the top roller 98 can be such that a cooperation in the tendency of forming the concave-shape is achieved by arranging roller 111 in a slightly higher plane than roller 110, as shown by the two dot-and-dash-lines 113, 114.

Obviously, an apparatus could be provided where the electric wire moves with regard to the plate-like member to be severed; in other words, a relative movement between the wire and the plate-like member must be provided.

In the several embodiments hereinabove described, the electromagnetic unit 79 is housed in recess 75, which is located in the rear face portion; however, nothing speaks against the possibility that the electromagnetic unit 79 is connected to the hardened front face 72.

It is also possible to coat the marginal vibration damping portion 73 with a hardening layer, for instance a vinylic layer, and to connect thereto a second electromagnetic unit (not shown) which is particularly operable in the high frequency range, so as to have a more pronounced 'sound reproduction for the high pitches. Thus, a more generic concept is that the diaphragm should have a stressed layer for increasing the quality of the sound production.

It will be obvious that modifications may be introduced in this invention upon carrying it out into practice as far as certain structural details are concerned but always without departing from the fundamental principles which are clearly specified in the following claims:

I claim:

1. A diaphragm to be used in sound transducers, comprising a strong, stiff, plastics plate-like member formed by a continuous structure of cells and having a sealed front face, a rear face and side faces connecting said front and rear faces, the cells defining said front face being under a higher stress than the successive cells defining said diaphragm from said front face towards said rear face, the stresses progressively decreasing from said front face towards said rear face, and the surface defining said front face being a hardened skin-like surface integral with said plate-like member and sealing said front face, said skin-like surface having been obtained by heat severing.

2. The diaphragm of claim 1, wherein said heat severed and sealed front face is concavely shaped.

3. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a tensioned sheetlike member adhered to said front face and a frame for said diaphragm, said diaphragm being connected to said frame.

4. The diaphragm of claim 3, wherein saidsheet-like member is also adhered to said side faces and said frame supports and maintains said diaphragm insubstantially flat position with the substantially straight front face.

5. The diaphragm of claim 4, wherein said rear face defines a marginal vibration damping portion circumscribing a pinna of the human ear shaped figure portion, said figure portion including a central portion which is stiffer than the remainder of the figure portion and which is located within a zone of the figure portion which is out of the geometric center thereof, said stiffer portion forming a center for collecting vibrations and an endless channel having a bottom wall adjacent said front face connecting the periphery of said figure portion with said marginal vibration damping portion.

6. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a sheet-like member adhered to said front face and a frame for said diaphragm, said diaphragm being connected to said frame.

'7. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a sheet-like member in front of said front face and a frame, said sheetlike member being supported by said frame, said diaphragm being connected to said frame and arranged beneath said sheet-like member in said frame.

8. The diaphragm of claim 1, wherein said rear face defines a marginal vibration damping portion circumscribing a figure portion, said figure portion including a central portion which is stiffer than the remainder of the figure portion and which is located within a zone of the figure portion which is out of the geometric center thereof, said stiffer portion forming a center for collecting vibrations. l

9. The diaphragm of claim 8, wherein said rear face includes an endless channel having a bottom wall adjacent said front face and connecting the periphery of said figure portion of said marginal vibration damping portion.

10. The diaphragm of claim 8, wherein said front face is substantially planar, thereby defining a substantially flat diaphragm.

l The diaphragm of claim 9, wherein said front face is substantially planar, thereby defining a substantially flat diaphragm. 

1. A diaphragm to be used in sound transducers, comprising a strong, stiff, plastics plate-like member formed by a continuous structure of cells and having a sealed front face, a rear face and side faces connecting said front and rear faces, the cells defining said front face being under a higher stress than the successive cells defining said diaphragm from said front face towards said rear face, the stresses progressively decreasing from said front face towards said rear face, and the surface defining saiD front face being a hardened skin-like surface integral with said plate-like member and sealing said front face, said skin-like surface having been obtained by heat severing.
 2. The diaphragm of claim 1, wherein said heat severed and sealed front face is concavely shaped.
 3. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a tensioned sheet-like member adhered to said front face and a frame for said diaphragm, said diaphragm being connected to said frame.
 4. The diaphragm of claim 3, wherein said sheet-like member is also adhered to said side faces and said frame supports and maintains said diaphragm in substantially flat position with the substantially straight front face.
 5. The diaphragm of claim 4, wherein said rear face defines a marginal vibration damping portion circumscribing a pinna of the human ear shaped figure portion, said figure portion including a central portion which is stiffer than the remainder of the figure portion and which is located within a zone of the figure portion which is out of the geometric center thereof, said stiffer portion forming a center for collecting vibrations and an endless channel having a bottom wall adjacent said front face connecting the periphery of said figure portion with said marginal vibration damping portion.
 6. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a sheet-like member adhered to said front face and a frame for said diaphragm, said diaphragm being connected to said frame.
 7. The diaphragm of claim 1, wherein said front face is substantially planar, said diaphragm being a substantially flat diaphragm, and including a sheet-like member in front of said front face and a frame, said sheet-like member being supported by said frame, said diaphragm being connected to said frame and arranged beneath said sheet-like member in said frame.
 8. The diaphragm of claim 1, wherein said rear face defines a marginal vibration damping portion circumscribing a figure portion, said figure portion including a central portion which is stiffer than the remainder of the figure portion and which is located within a zone of the figure portion which is out of the geometric center thereof, said stiffer portion forming a center for collecting vibrations.
 9. The diaphragm of claim 8, wherein said rear face includes an endless channel having a bottom wall adjacent said front face and connecting the periphery of said figure portion of said marginal vibration damping portion.
 10. The diaphragm of claim 8, wherein said front face is substantially planar, thereby defining a substantially flat diaphragm.
 11. The diaphragm of claim 9, wherein said front face is substantially planar, thereby defining a substantially flat diaphragm. 